NO343583B1

NO343583B1 - System and method for removal of waste from fish cages

Info

Publication number: NO343583B1
Application number: NO20171622A
Authority: NO
Inventors: Jarle Ragnhildstveit
Original assignee: Lift Up As
Priority date: 2017-10-11
Filing date: 2017-10-11
Publication date: 2019-04-08
Also published as: NO20171622A1

Description

System and method for removal of waste from fish cages

The present invention relates to a system and a method for removal of waste such as sunken particles and sunken farmed organisms such as dead fish from a net cage. The net cage is preferably a fish cage in the sea, but the system may also be used in fish farms onshore.

Background

The annual production of salmonids in Norway was about 1.3 millions tons in 2012, 99 % being Atlantic salmon and trout. The production of salmon is at present mainly based on fish cage aquaculture in the sea, where salmon are cultivated in large net cages. During the production different forms of waste will be produced in the fish cage, such as dead fish, faeces, unconsumed feed etc. In this application, the dead fish and other waste will be referred to as "bottom waste" as the waste falls to the bottom of the net cage.

Numerous systems exist for removal of dead fish and other waste being collected in the bottom of a net cage. The most used system in Norway is from Lift Up AS and comprises a collector positioned at the bottom of the net inside the net cage, and an air lift pump comprising a compressor which supplies pressurized air to the collector. Bottom waste will naturally sink to the bottom of the fish cage and gather in the area around the collector. By using an air lift pump connected to the collector, the waste is pumped through a pipe system to a receiving section on the surface for removal and/or further treatment. The principles of the system from Lift Up are well known for persons skilled in the art and are e.g. described in WO 2012/064201. Such a system to pump dead fish and other waste is in the following referred to as an "air lift pump".

The collector in the system of Lift Up is designed with a conical lower face resting against the bottom of the net cage when the collector is correctly positioned. The tip of the net cage is the deepest point of the net bag, and the bottom of the net bag is normally reinforced so that it may carry the collector without risk of tearing and damaging of the net. A collector may typically weigh from 450 to 1000 kg. The ballast weight is often galvanized steel being positioned in cavities of the collector. A system for positioning such a collector is given in NO339199.

There is a problem that the collectors may move out of their position, for instance because they are not properly installed, due to bad weather and heavy sea, or due to different operations on the net cage. When the collector rests or hits the net in areas which are not reinforced, it may cause holes or other damages to the net so that the risk for fish escaping increases. Escaping of fish has large negative consequences for the fish farmers and for the environment as such. It is a well-known issue that farmed fish may infect wild stocks with diseases mostly known among farmed fish.

Some fish cages do not have a conical bottom, but a more flat design, and thus the positioning of the known collector from Lift Up AS is a problem. In cages having a conical bottom the collector will naturally be positioned in the centre due to the weight, but when the bottom is nearly flat the collector may move due to weather and current. Therefore, the know systems have not been installed in such cages, and the bottom waste has been removed by other means.

One object of the present invention is therefore to provide an improved and safer device for removing waste collected at the bottom of a fish cage. Further, it is an object that the device should be operative even if there are winds and/or current in the area around the net cage. Another object is that it should be possible to automatize the device, and preferably such that no manpower is required at the site. Yet another object is that the device should be easy and quick to install and remove, not cause damage to the fish or net cage, nor interfere with equipment normally installed in a fish farm.

The invention

The objects are achieved with a system according to claim 1, and a method according to claim 8. Further advantageous features are given in the corresponding dependent claims.

The system and method according to the invention are designed to be used on a traditional net cage. A traditional net cage comprises a floating collar in the surface of the sea, preferably having a walkway and a handrail. The floating collar provides buoyancy to the whole net cage. The net cage traditionally also comprises a bag of net connected to, and hanging from, the floating collar, which encages the organisms to be farmed. At the bottom of the net cage there is traditionally a bottom weight for maintaining the shape of the net bag and for stretching it out to its maximum volume. The net cage is normally moored to the sea bed by a number of lines. The net cage may both be a single cage at the location or a part of a large farming plant with many net cages.

A system for removing waste from the bottom of a net cage according to the present invention, comprises a waste pipe and a pump, wherein

- a first end of the waste pipe is arranged to be connected to a receiving section and a second end has a free opening for removing waste,

- the pump is an air lift pump, having an air pipe connected to the second end of the waste pipe,

- the second end of the waste pipe is provided with one or more organs to avoid that the second end gets in contact with the net of the net cage, and

- the second end of the waste pipe is connected to a line running to a guide at the bottom of the net cage, and further to a pulling system.

A receiving section receives the water and bottom waste removed from the bottom of the fish cage, and transports it for further treatment and processing. Such receiving sections are well known to a skilled person and may be adapted to specific requirements for the location and/or farm.

The first end of the waste pipe may be fastened to a floating collar of the fish cage and connected to a receiving section only when the waste should be removed. In these cases the first end of the pipe should preferably be in or above the surface of the water to ease the connection to the receiving section. In a preferred embodiment is the first end of the waste pipe fastened to a pipe fitting, such as an elbow pipe joint, at a hand rail of the floating collar. The receiving section may then be on a vessel docking the fish farming plant, and may be connected to the waste pipe via the pipe fitting.

In an alternative embodiment, the first end of the waste pipe may be connected directly to a receiving section arranged on the net cage or farming plant. In yet another alternative embodiment, the waste pipe is connected directly to a receiving section on a vessel, and the whole system for removal of waste is installed in the net cage every time the waste should be removed.

Whenever the second end of the waste pipe is below water, and air is supplied into the second end by the air pipe, the air will rise to the surface inside the waste pipe and the free opening will function as a vacuum cleaner head. This is the basic function of an air lift pump. As described above, the pump may be a compressor supplying air to the second end of the waste pipe through the air pipe. Therefore, whenever the phrase "pump" is used, compressors should be included.

The air pipe connected to the second end of the waste pipe is preferably arranged along and fastened to the outside of the waste pipe, in order to reduce the number of lines, pipes and cables running in the fish cage. The air from the air pipe should preferably be supplied into the second end of the waste pipe at a distance from the free opening in order to create the desired suction in the waste pipe. Use of air lift pumps are well known for removal of waste from the bottom of a fish cage, and a skilled person would be able to find the suitable distance.

The second end of the waste pipe is provided with one or more organs to prevent contact between the waste pipe and the net of the net cage. If the net comes into contact with the free opening, the net may be partly sucked into the waste pipe and be destroyed. The organs also prevent that the end of the waste pipe tangles with the net or other ropes and lines in the net cage, and causes damage to the system or net cage. In a preferred embodiment is the organ an U-shaped obstacle arranged across and perpendicular to opening of the waste pipe, protruding away from the opening. The obstacle will prevent that the net may be sucked into the opening. The obstacle is preferably made of a metal tube, bent to the desired shape.

The line running from the second end of the waste pipe to a guide at the bottom of the net cage and further to a pulling system, may be running from the guide through the net cage and above the surface of the sea, before it is connected to the pulling system. The pulling system may be arranged on the surface of the net cage, such as on the walk way, preferably on the opposite side of the first end of the waste pipe. In this case, the guide at the bottom of the fish cage may be a loop, pulley, castor or the like arranged to guide the line to the surface again. The guide is fastened to the bottom and/or the anchoring of the cage, and when the pulling system pulls the line, the second end of the waste line will be pulled to the bottom of the cage. The pulling system is preferably a winch, but may also be manpower or any other suitable system.

In an alternative embodiment, the guide let the line through the bottom of the net cage, and further to the pulling system. In this case the guide may simply be a reinforced hole or funnel in the net, and the pulling system may be arranged anywhere, even submersed. In yet other embodiments the system comprise several guides between the second end of the waste line and the pulling system.

As said above, the line is running from the second end of the waste pipe to a guide at the bottom of the fish cage, and further to the pulling system. When the pulling system pulls the line, the second end of the waste pipe having the free opening, will be pulled towards the bottom of the fish cage. Once the opening is in the vicinity of the bottom waste at the bottom of the fish cage, the pump is started and the bottom waste will be sucked into the opening of the pipe and removed from the net cage.

A camera such as a video camera may be mounted at or close to the second end of the waste pipe, to monitor the remaining amount of waste during suction. Such a camera must cooperate with a device on the surface of the sea, enabling the operator to make decisions when to stop pumping. A light is preferably also mounted on the second end of the waste pipe, to enlighten the area where the suction is used. This will improve the pictures or film to be assessed from the surface and the operator may control the location of the second end of the waste pipe and the suction optimally.

When the waste is removed, the pump is stopped, and the pulling system unwinds or otherwise slacks the line. The waste pipe may then move in the fish cage in relation to water current and wind, and the danger of damage to the net is reduced. The distance which the second end of the pipe may move depends on the length of the line being released from the pulling system.

In a preferred embodiment, one or more buoyancy member are fastened to the waste pipe, preferably to the upper half of the waste pipe. The buoyancy member should have sufficient buoyancy to keep the whole waste pipe in the water, but without creating substantial counter force when the pulling system pulls the line. In a more preferred embodiment, the system comprises two buoyancy members connected to the waste pipe at a distance from each other. The buoyancy members will lift the second end of the waste pipe from the bottom of the net cage once the pulling system slacks the line, and thus is the chances of contact between the net and the second end of the waste pipe reduced.

Preferably at least parts of the waste pipe should be flexible, meaning that it may fold at arbitrary positions. When the system is not in use, the flexible parts of the pipe may collapse and fold up on itself, leaving few or no hard surfaces which may harm the net. The second end of the pipe, comprising the free opening, should preferably not be flexible, as the opening needs to be kept open when the air pipe supplies air to the waste pipe.

The waste line may be produced in several parts, wherein the parts are mounted to constitute a continuous tube before use. For instance may the end of the waste line, having the protective elements be produced separately from the flexible pipe. The flexible parts of the pipe also makes it easier to handle and transport the system.

The invention also relates to a method for removing waste from the bottom of a fish cage, by using a system as described above. The method comprises the following steps:

- pulling the line with the pulling system until the second end of the waste pipe is close to the bottom of the fish cage, and

- generating a suction through the waste pipe by supplying air into the opening of the second end of the waste pipe by means of the air pipe.

When water, air and waste are sucked into the waste pipe, the different parts of the waste pipe will distend, and all parts of the pipe will unfold. The pipe will remain expanded as long as the pump is running.

If the system is not stationary arranged in the fish cage, then the method also comprises the steps for:

- attaching the line running through the guide at the bottom of the fish cage to the second end of the waste pipe, and/or

- attaching the pump to the air pipe and,

- attaching the first end of the waste pipe to the receiving section.

If the system is not arranged in the fish cage at all times, for instance if the waste pipe is not in the fish cage, then the system must be installed in the fish cage before it can remove any waste. In other embodiments, the waste pipe and air pipe is installed in the fish cage, but the pump and receiving system is not connected to the pipes at all times, and must thus be attached to the system before waste may be removed. The waste pipe, the pump, the receiving section and/or other parts of the system may for instance be partly or fully installed on a vessel, wherein the vessel docks at the fish cage whenever waste should be removed.

When sufficient waste is removed, the method comprises the following steps,

- shutting down the pump by stopping supply of air into the second end of the waste pipe and

- slackening the line from the pulling system.

In order to decide when the opening is at sufficient distance from the bottom waste, one may for instance measure the length of the pulled line. In order to decide when sufficient waste is removed, one may for instance inspect the pumped water in the receiving section. In another embodiment, the second end is provided with a camera and possibly light as described above, which will assist the operator in one or both of these decisions.

When air is no longer supplied to the waste pipe, the suction will disappear and the waste pipe will again be able to fold and collapse at any convenient places. By slacking the line from the pulling system, less stress will be acting on the waste pipe at the same time as it is able to float and move together with the water and surrounding installations. This reduces the risk for damages both to the cage and to the system.

If the system is not stationary arranged in the fish cage, the method may further comprise the following steps after sufficient waste is removed:

- pulling the waste pipe until the second end is above the surface of the water, - unfastening the line from the second end, and attaching the line to the floating collar of the fish cage, and/or

- unfastening the pump from the air pipe and

- unfastening the first end of the waste pipe from the receiving section.

If the waste pipe and air pipe should stay in the fish cage, then there is no reason to pull the waste pipe until the second end is above the surface of the water, neither to unfasten the line from the second end. However, if the waste pipe and air pipe should be removed from the fish cage, then the line should be unfastened and attached to the fish cage, preferably to the floating collar, in order to ease the next installation of a waste pipe.

Examples

The invention will now be described with the help of the enclosed figures, showing a system for removing waste from the bottom of a fish cage, according to the present invention. The different parts of the figure are not necessarily in scale to each other, as the figure is merely for illustrating the invention.

The following description of an exemplary embodiment refers to the drawings, and the following detailed description is not meant or intended to limit the invention. Instead, the scope of the invention is defined by the appended claims.

Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.

The invention will in the following be described with reference to the enclosed figures, where

Figure 1 shows a cross section of a fish cage, having the system according to the invention installed in removal position, and

Figure 2 shows a cross section of the fish cage shown in Figure 1, but the system according to the invention is shown in relaxed position, and

Figure 3 shows details of the lower end of the waste pipe in perspective.

Figure 1 and 2 show a cross section of a net cage having a floating collar 1 with a handrail 2, a net bag 3, and a bottom weight 4 for keeping the net cage distended. The system according to the present invention comprises a waste pipe 5 having a first end 5a fastened to the handrail 2 of the floating collar, and a second end 5b having a free opening 7. The first end 5a is arranged to be connected to a receiving section (not shown) which may be somewhere on the farming plant or on a vessel. The system also comprises a pump being an air-lift pump, having an air-pipe 8 supplying air to the second end 5b of the waste pipe 5, and a compressor (not shown).

The second end 5b of the waste pipe is shown in detail in Figure 3, and is provided with a cleaner head 6 having a conical expansion wherein the radius of the opening 7 of the cleaner head is larger than the radius of the waste pipe. This is simply to cover a larger area at the opening, which will be obvious to a person skilled in the art. The second end 5b of the waste pipe is further provided with two ears 13 being a part of a quick release coupling, for connecting the end 5b of the waste pipe to the cleaner head 6.

The cleaner head 6 is provided with five protective organs; four fenders or hoops 9 arranged circumferential around the opening 7, and one U-shaped pipe 10 arranged across and perpendicular to the opening 7, protruding in the opposite direction of the suction. The protective organs are arranged to avoid that the cleaner head 6 and especially the opening 7 of the waste pipe gets in contact with the net of the net bag 3. The four hoops 9 are also protecting cameras and lights (not shown) arranged on the outside of the cleaner head, inside the hoops. In a preferred embodiment is the U-shaped pipe fastened to the cleaner head on the outside of the opening, and the hoops 9 are covering the fastening points. In this way the hoops 9 are also preventing that the cleaner head 6 gets tangled in ropes and lines in the fish cage.

When the system is arranged in a fish cage as shown in Figures 1 and 2, the second end of the waste pipe is connected to a line 11 running to a guide at the bottom of the fish cage. The line may be attached at any convenient place of the end 5b of the waste line or the cleaning head 6, and in a preferred embodiment is the line attached to the cleaner head at the same place as the protecting U-shaped pipe.

In the shown embodiment, the guide at the bottom of the net cage is a loop at the top of the bottom weight 4, and the line 11 is guided back to the surface of the water and further to a pulling system (not shown) on the walk way of the floating collar. In order to reduce the wear of the line when pulled through the loop, the pulling system should be arranged on the opposite side of the first end 5a of the waste line.

Two buoys 14 are attached to the waste line 5. These buoys add sufficient buoyancy to the waste line 5 to lift the cleaner head 6 from the bottom area of the fish cage, but not enough to represent a counter force to the pulling system when the waste line is pulled to the bottom of the cage.

When waste at the bottom of the fish cage should be removed, the pulling system pulls the line 11, the line will be pulled through the guide, and pull the second end 5b of the waste line towards the bottom of the cage. The pulling system is arranged to pull the line only a predetermined distance, and once the pulling system stops, the cleaner head 6 is close to the bottom and the opening 7 is facing the bottom waste. Then air is supplied to the waste pipe 5 through the air pipe 8 arranged on the cleaner head 6, and suction will occur through the opening 7. When sufficient waste is removed, the supply of air is shut off, the suction will decline and finally disappear. Then the pulling system loosens the same amount of the line, and the cleaner head 6 of the waste line is removed from the bottom area by the buoyancy in the buoys 14.

The example above is given to illustrate the invention and should not be used to interpret the following claims limiting. The scope of the invention is not limited by the example give above, but the enclosed claims..

Claims

1. System for removing waste from the bottom of a net cage, comprising a waste pipe (5) and a pump, characterized in that

- a first end (5a) of the waste pipe is arranged to be connected to a receiving section and a second end (5b) has a free opening (7) for removing waste,

- the pump is an air lift pump, having an air pipe (8) connected to the second end (5b) of the waste pipe,

- the second end of the waste pipe is provided with one or more protective organs (10) to avoid that the second end gets in contact with the net of the net cage, and

- the second end of the waste pipe is connected to a line (11) running to a guide at the bottom of the net cage, and further to a pulling system.

2. System according to claim 1, characterized in that the first end of the waste pipe (5) is fastened to a floating collar (1) of the net cage.

3. System according to claim 1 or 2, characterized in that the line (11) is further running from the guide at the bottom of the net cage, through the net cage and to the floating collar (1) where it is connected to the pulling system.

4. System according to claim 3, characterized in that the pulling system is arranged at the floating collar (1) , preferably on an opposite side of the first end (5a) of the waste pipe.

5. System according to claim 1, characterized in that the protective organs are a U-shaped obstacle, arranged across and perpendicular to the opening of the waste pipe, protruding away from the opening (7).

6. System according to any one of the proceeding claims, characterized in that one or more buoyancy members (14) are attached to the waste pipe (5), preferably at an upper half of the waste pipe.

7. System according to any one of the proceeding claims, characterized in that the guide is a loop, pulley, castor or the like fastened at the bottom of the net cage.

8. Method for removing waste from the bottom of a net cage, by using a system according to claim 1, characterized by comprising the following steps:

- pulling the line (11) with the pulling system until the second end (5b) of the waste pipe is close to the bottom of the net cage (3),

- generating a suction through the waste pipe by supplying air into the opening (7) of the second end (5b) of the waste pipe by means of the air-pipe (8).

9. Method according to claim 8, characterized by comprising the following steps before the steps of claim 8, when the system is not stationary arranged in the net cage:

- attaching the line (11) running through a guide at the bottom of the net cage to the second end (5b) of the waste pipe, and/or

- attaching the pump to the air pipe (8), and

- attaching the first end (5a) of the waste pipe to a receiving section.

10. Method according to any one of claim 8 and 9, characterized by comprising the further steps once the waste is removed,

- shutting down the pump by stopping supplying air into the second end of the waste pipe and

- slackening the line from the pulling system.

11. Method according to claim 10, characterized by comprising the following steps after the steps of claim 10, when the system is not stationary arranged in the net cage:

- pulling the waste pipe until the second end is above the surface of the water,

- unfastening the line from the second end, and attaching the line to the floating collar of the net cage, and/or

- unfastening the pump from the air pipe and

- unfastening the first end of the waste pipe from the receiving section.